1. Field of the Invention
The present invention relates to a press working machine, and more specifically, it relates to a press working machine which can be readily employed for molding/joining metal plates, press-fitting/assembling machine parts, and the like.
2. Description of the Background Art
There have generally been made various proposals in relation to a method of embodying an area (low-thrust/high-speed area) requiring a high speed with a moderate thrust and an area (high-thrust/low-speed area) requiring a high thrust with a moderate speed through a press working machine which is supplied with only an air pressure serving as driving force therefor.
FIGS. 11 to 14 show a press working machine of a system utilizing the principle of a pressure intensifier (air hydraulic booster) for obtaining a hydraulic pressure which is intensified by the ratio of an area of an air cylinder to that of a piston, for example.
In a pullback position shown in FIG. 11, a main valve (a) is switched to supply air to a piston chamber (b), while discharging air from the piston chamber (c). Thus, a working piston 31 is moved to a position shown in FIG. 12 at a low thrust and a high speed.
After this high-speed movement process of the working piston 31, a feed piston 33 which is driven by a spring 42 feeds oil from an accumulator 41 to a high-pressure chamber 35 under pressure. Thus, a pneumatic valve (d) is started by the resistance, to introduce compressed air into a booster piston chamber (e).
Thereafter a plunger 33 of a booster piston 32 passes through the high-pressure chamber 35 as shown in FIG. 13 to divide the high-pressure chamber 35 into a working area and an oil accumulator, and compresses the oil in the working area to a constant high pressure.
Thereafter the working piston 31 is supplied with a high-thrust stroke due to displacement of the oil by the plunger 33, as shown in FIG. 14. In this press working machine, the working piston 31 is moved by a distance which is proportionate to the volume of the displaced oil.
In a return stroke, the main control valve (a) is so switched that the pneumatic valve (d) automatically ventilates the chamber (e), and the working piston 31 and the booster piston 32 are immediately returned to the initial positions shown in FIG. 11.
FIGS. 15 to 17 show another press working machine utilizing a converter.
In this press working machine, a port P.sub.3 first sucks air in the state shown in FIG. 15, to advance a hydraulic piston 50 through a hydraulic pressure converter 48 in a rapid traverse manner. Then, air is supplied through a port P.sub.1 to advance a booster piston 51 at a high thrust by a hydraulic pressure which is intensified by the Pascal's principle (twice the pneumatic booster ratio) as shown in FIG. 16.
Then, air is supplied through ports P.sub.2 and P.sub.4 while the remaining ones are converted to discharging states as shown in FIG. 17, whereby both of the hydraulic piston 50 and the booster piston 51 recover to the initial states shown in FIG. 15 at a high speed.
However, each of the aforementioned conventional press working machines obtaining high thrusts through hydraulic pressures has the following problems:
(1) The pressure obtained in the pressure intensifying process is limited due to dependence on the Pascal's principle. Namely, the maximum reachable thrust is about 40 tons, since the cylinder area ratio is about 1:40 at the most. PA1 (2) The inner diameter of the air cylinder exceeds 100 mm as described above, and hence the apparatus is increased in scale due to the large cylinder dimensions. PA1 (3) In order to attain a high thrust, an air pressure of 5 to 10 kgf/cm.sup.2 is necessary. Thus, it is necessary to intensity a supplied air pressure (up to 5 kgf/cm.sup.2) which is employed in an ordinary factory.
In order to attain a higher thrust, further, it is necessary to increase the inner diameter of the air cylinder to at least 100 mm. Thus, the volume of consumed air is extremely increased.